{"title":"Intersection-union家庭","authors":"Peter Frankl , Jian Wang","doi":"10.1016/j.jcta.2025.106100","DOIUrl":null,"url":null,"abstract":"<div><div>Let <span><math><msup><mrow><mn>2</mn></mrow><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></msup></math></span> denote the power set of the <em>n</em>-set <span><math><mo>[</mo><mi>n</mi><mo>]</mo><mo>=</mo><mo>{</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>n</mi><mo>}</mo></math></span>. For positive integers <span><math><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi></math></span>, <span><math><mi>n</mi><mo>≥</mo><mi>p</mi><mo>+</mo><mi>q</mi></math></span> let <span><math><mi>m</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></math></span> denote the maximum of <span><math><mo>|</mo><mi>F</mi><mo>|</mo></math></span> for a family <span><math><mi>F</mi><mo>⊂</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></msup></math></span> satisfying <span><math><mo>|</mo><mi>F</mi><mo>∩</mo><mi>G</mi><mo>|</mo><mo>≥</mo><mi>p</mi></math></span> and <span><math><mo>|</mo><mi>F</mi><mo>∪</mo><mi>G</mi><mo>|</mo><mo>≤</mo><mi>n</mi><mo>−</mo><mi>q</mi></math></span> for all <span><math><mi>F</mi><mo>,</mo><mi>G</mi><mo>∈</mo><mi>F</mi></math></span>. The exact value of <span><math><mi>m</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></math></span> has been known for half a century in the case <span><math><mi>p</mi><mo>=</mo><mn>1</mn></math></span> or <span><math><mi>q</mi><mo>=</mo><mn>1</mn></math></span>. Bang, Sharp and Winkler determined it in the case <span><math><mi>n</mi><mo>−</mo><mi>p</mi><mo>−</mo><mi>q</mi><mo>≤</mo><mn>3</mn></math></span>. The aim of the present paper is to establish the exact value of <span><math><mi>m</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></math></span> for <span><math><mi>n</mi><mo>≥</mo><msup><mrow><mo>(</mo><mi>n</mi><mo>−</mo><mi>p</mi><mo>−</mo><mi>q</mi><mo>+</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>3</mn></mrow></msup></math></span> and also for <span><math><mi>n</mi><mo>−</mo><mi>p</mi><mo>−</mo><mi>q</mi><mo>=</mo><mn>4</mn></math></span>.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"217 ","pages":"Article 106100"},"PeriodicalIF":1.2000,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Intersection-union families\",\"authors\":\"Peter Frankl , Jian Wang\",\"doi\":\"10.1016/j.jcta.2025.106100\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>Let <span><math><msup><mrow><mn>2</mn></mrow><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></msup></math></span> denote the power set of the <em>n</em>-set <span><math><mo>[</mo><mi>n</mi><mo>]</mo><mo>=</mo><mo>{</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>n</mi><mo>}</mo></math></span>. For positive integers <span><math><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi></math></span>, <span><math><mi>n</mi><mo>≥</mo><mi>p</mi><mo>+</mo><mi>q</mi></math></span> let <span><math><mi>m</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></math></span> denote the maximum of <span><math><mo>|</mo><mi>F</mi><mo>|</mo></math></span> for a family <span><math><mi>F</mi><mo>⊂</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></msup></math></span> satisfying <span><math><mo>|</mo><mi>F</mi><mo>∩</mo><mi>G</mi><mo>|</mo><mo>≥</mo><mi>p</mi></math></span> and <span><math><mo>|</mo><mi>F</mi><mo>∪</mo><mi>G</mi><mo>|</mo><mo>≤</mo><mi>n</mi><mo>−</mo><mi>q</mi></math></span> for all <span><math><mi>F</mi><mo>,</mo><mi>G</mi><mo>∈</mo><mi>F</mi></math></span>. The exact value of <span><math><mi>m</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></math></span> has been known for half a century in the case <span><math><mi>p</mi><mo>=</mo><mn>1</mn></math></span> or <span><math><mi>q</mi><mo>=</mo><mn>1</mn></math></span>. Bang, Sharp and Winkler determined it in the case <span><math><mi>n</mi><mo>−</mo><mi>p</mi><mo>−</mo><mi>q</mi><mo>≤</mo><mn>3</mn></math></span>. The aim of the present paper is to establish the exact value of <span><math><mi>m</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></math></span> for <span><math><mi>n</mi><mo>≥</mo><msup><mrow><mo>(</mo><mi>n</mi><mo>−</mo><mi>p</mi><mo>−</mo><mi>q</mi><mo>+</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>3</mn></mrow></msup></math></span> and also for <span><math><mi>n</mi><mo>−</mo><mi>p</mi><mo>−</mo><mi>q</mi><mo>=</mo><mn>4</mn></math></span>.</div></div>\",\"PeriodicalId\":50230,\"journal\":{\"name\":\"Journal of Combinatorial Theory Series A\",\"volume\":\"217 \",\"pages\":\"Article 106100\"},\"PeriodicalIF\":1.2000,\"publicationDate\":\"2025-08-14\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Combinatorial Theory Series A\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0097316525000950\",\"RegionNum\":2,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Combinatorial Theory Series A","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0097316525000950","RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
Let denote the power set of the n-set . For positive integers , let denote the maximum of for a family satisfying and for all . The exact value of has been known for half a century in the case or . Bang, Sharp and Winkler determined it in the case . The aim of the present paper is to establish the exact value of for and also for .
期刊介绍:
The Journal of Combinatorial Theory publishes original mathematical research concerned with theoretical and physical aspects of the study of finite and discrete structures in all branches of science. Series A is concerned primarily with structures, designs, and applications of combinatorics and is a valuable tool for mathematicians and computer scientists.